1. Field of the Invention
The present invention broadly relates to video data transmission apparatus having a frame memory and, more particularly, to a video data transmission apparatus for recording a plurality of batches of video information or data which have been transmitted or received. The present invention also is concerned with a video data transmission apparatus for backing up video data.
2. Description of the Related Art
A description will be given of a first known type video data transmission apparatus.
Transmission of video data through a high-speed digital circuit network, e.g., ISDN (Integrated Service Digital Network) has become popular in recent years. Such transmission is generally conducted by converting video data into digital video data, storing the digital video data in a semiconductor memory such as a frame memory and then outputting the digital video data to a circuit network through a MODEM (Modulation and Demodulation Device).
FIG. 1 shows an example of such a video data transmission apparatus. Referring to FIG. 1, a control program stored in a program memory unit 115 is executed by a system control unit 113. A work area necessary for the system control unit 113 to execute the control program is reserved in a random access memory unit 116. An address decoder unit 114 selects one of the program memory unit 115, random access memory unit 116 and a frame memory unit 117 in accordance with an address value output from the system control unit 113.
Video data which have been input through an input terminal 101 are processed by a signal processing unit 102 and the processed signals are converted by an A/D conversion unit 103 into discrete digital video data which are then latched by a latch unit 104. The digital video data is stored in the frame memory unit 117 via a data bus, under the control of the system control unit 113.
On the other hand, when digital video data stored in the frame memory unit 117 are transmitted through a circuit network, the digital video data is sent to a MODEM 111 together with additional data for communication control, by the operation of the system control unit 113 in accordance with a predetermined communication protocol. The digital video data is then sent to the circuit network (not shown) via the circuit line terminal 109 under the control of an NCU (network control unit), after an operation to match the electrical characteristics of the circuit network. Transmission of the next batch of video data is then conducted after the next batch of signals is stored in the frame memory unit 117 as is the case of the transmission of the preceding batch of signals.
The digital video data stored in the frame memory unit 117 are then latched by a latch unit 108 and are converted into analog signals by a D/A conversion unit 107, and these analog signals are processed by a signal processing unit 106. The processed signals are then output from an output terminal 105 to form an image on a display which is not shown.
In the known video data transmission apparatus as described, transmission is conducted such that, after the transmission of a batch of signals is completed, the next batch of signals is stored in the frame memory 117. Therefore, video data which have been transmitted can not be confirmed at the transmitting station or at the receiving station.
Furthermore, when reproduction of the same transmitted video data is to be conducted both at the transmitting station and the receiving station, a voice message has to be used to inform, from one station to the other, the index of the transmitted video data selected by the one station or the time record of transmission of such video data.
A description will now be given of a second known type of apparatus.
Most current video devices are battery-driven, in order to cope with the demands for use outdoors and for greater portability. In such apparatuses, it is very important to minimize electrical power consumption. The requirement for reduction in electrical power consumption is not severe in devices for storing ordinary information other than video information, since in such a case the amount of data is so small that the information can be safely stored in, for example, in a main memory of a CPU, with continued supply of little electrical power to at least such a main memory.
In the case of video information, however, the amount of the data is so large that storage of input video data in a video memory requires supply of a large amount electrical power to the video memory. Therefore, the video information cannot be held for a long time when power is derived from batteries.
Therefore, known video devices, e.g., video cards for monitor output, are not constructed to keep video data stored in a video memory. When the apparatus is re-started after turning off the power, it is necessary to rewrite the necessary video data in the video memory. In other words, the original video information is lost when the video memory is not rewritable.